The iron uptake of Japanese has been maintaining about 100% sufficiency rate for requirement ever since 1975 and iron is deemed as one of the essential nutritional elements that must be carefully taken up with meals. In world-wide point of view, individuals in advanced industrial countries suffer a deficiency of iron, thus supply of iron enriched foods or medicines for persons with anemic tendency and pregnant and breast feeding females is desired. However, iron salts generally used for enrichment such as iron sulfate or iron citrate produce of iron characteristic astringent taste and adverse reactions such as disturbance of gastrointestinal mucosa, thus, the amount to be added is limited. Organic iron compounds such as heme-iron also have problems of taste such as metallic and fishy taste, and their addition to foods face many restricted conditions.
Addition of milk casein, amino acids or casein phosphopeptide or the like has been tried for stimulation of iron absorption (Japanese Laid-open Patent Application No. 162843 (1984)). However, these methods could not diminish the astringent taste of iron compounds, furthermore, reduced amount of addition of iron failed to diminish the astringent taste of iron.
The inventors of the present invention already succeeded to reduce characteristic astringent taste of iron by combining iron and casein (Japanese Laid-open Patent Application No. 83400 (1990)). However, the prepared iron casein complex has poor heat stability exhibited iron characteristic astringent taste following heat sterilization at 90.degree. C. for 10 minutes or 120.degree. C. for 2-3 seconds, or retort sterilization. Therefore, application of the iron casein complex to foods demand sterilization of production line and causes poor cost effectiveness. The characteristic astringent taste of the iron casein complex caused by heat sterilization may be due to the release of iron from weak iron and casein binding, and formation of iron hydroxides. Thus, a more firm heat resistant binding of iron and casein without exhibiting iron characteristic astringent taste even following heat sterilization was developed.
This invention aims to provide pharmaceutical iron preparations as food additives free from iron characteristic astringent taste even following heat sterilization. That is, one object of the present invention is to provide carbonic acid- and/or hydrogencarbonic acid-iron-casein complexes and methods for preparation thereof.